1. Field of the Invention
The present invention relates generally to video signal processing apparatus and, more particularly is directed to apparatus for processing a video signal when recording the same and when reproducing the video signal, as in a video disc player.
2. Description of the Prior Art
In the prior art, a standard video signal, for example, according to the NTSC system, and which will be hereinafter referred to as a composite video signal, is frequency modulated and then recorded on a video disc. As shown in FIG. 1, in a video diso player 1 for reproducing such standard video signal recorded on a video disc, an optical pick-up (not shown) reproduces the frequency-modulated composite video signal which is then frequency-demodulated in a circuit 4. A component of the demodulated composite video signal S.sub.STV situated in a chroma band is then extracted from the demodulated composite video signal by a bandpass filter circuit 5, and the resulting extracted signal component is processed by a comb-type filter circuit 6 to provide a chroma signal S.sub.C separated from the composite video signal. Further, the separated chroma signal S.sub.C is subtracted from the composite video signal S.sub.STV in a subtracting circuit 7 which thereby provides a separated luminance signal S.sub.Y.
In a video apparatus, such as, a camera or image pick-up apparatus or the like, an imager signal is frequently not converted to a composite video signal, but rather is outputted as a component video signal, that is, as separated luminance and chrominance signals. In the case of a component video signal, as contrasted with the usual composite video signal, a luminance signal of wide frequency band can be provided for obtaining a displayed picture therefrom of high resolution. In other words, if a component video signal including a luminance signal of wide frequency band is recorded on a video disk, then a picture of high resolution or image quality may be reproduced by a video disc player. However, when recording a component video signal including a luminance signal of wide frequency band on a video disc, it is necessary to establish compatibility between such socalled high resolution video disc and a conventional or prior-art video disc on which a composite video signal is recorded. To this end, it has been proposed that, as shown on FIG. 2, a luminance signal S.sub.YH of wide frequency band and a chroma signal S.sub.CH, which form a component video signal, be added by an adding circuit 8 for providing a signal S.sub.REC which is then recorded on the video disc. When such simple proposal is followed, interference between the luminance signal S.sub.YH and the chroma signal S.sub.CH can not be avoided so that problems, such as, cross-color, dot interference and the like do occur and the quality of the resulting displayed picture is deteriorated.
In order to solve the foregoing problems, it has been proposed, for example, as shown on FIG. 3, to superimpose a chroma signal S.sub.CL upon a relatively wide band luminance signal S.sub.YH through the use of comb-type filter circuits 9 and 10. More specifically, the chroma signal S.sub.CL, which is initially limited to a band similar to the frequency band of the chroma in the standard composite video signal, is fed to the comb-type filter circuit 9 in which signal components having frequencies (n-1) f.sub.H, nf.sub.H, (n+1) f.sub.H, . . . are suppressed so as to provide a chroma signal S.sub.CK having a comb-like frequency characteristic as shown in full lines on FIG. 4, and wherein f.sub.H represents the horizontal synchronizing frequency.
The wide band luminance signal S.sub.YH is supplied to a band-pass filter circuit 11 which has a pass-band equal to the frequency band of the chroma signal S.sub.CL, and which is hereinafter referred to as the "chroma band". The component of the luminance signal S.sub.YH in the chroma band, that is, the component of the luminance signal S.sub.YH passing through the band-pass filter circuit 11, is supplied to the comb-type filter circuit 10 which has the same characteristic as the comb-type filter circuit 9. A subtracting circuit 12 subtracts the output of the comb-type filter circuit 10 from the luminance signal S.sub.YH, and thereby suppresses a signal component of the frequencies (n-1/2)f.sub.H (n+1/2) f.sub.H . . . within the chroma band of the luminance signal S.sub.YH. Therefore, at the output of the subtracting circuit 12, there is obtained a luminance signal S.sub.YK which is frequency-interleaved in respect to the chroma signal S.sub.CK, and which is represented by the dotted line on FIG. 4. When such luminance signal S.sub.YK and the chroma signal S.sub.CK are added in an adding circuit 13, there is obtained, as the output from the adding circuit 13, a video signal S.sub.ADD having a frequency characteristic corresponding with that of the standard composite video signal in the frequency band below the chroma band, and which contains luminance information in a frequency band above the chroma band.
Since, the prior art video disc player 1 (FIG. 1) is arranged to process the signal component in the band lower than the chroma band, such player can be employed for playback of a video disc on which the video signal S.sub.ADD has been recorded rather than the standard composite video signal S.sub.STV (FIG. 1). Thus, deterioration of the quality of the displayed picture can be avoided and the compatibility of a video disc recorded with the video signal S.sub.ADD, that is, a signal which includes a wide band luminance signal, with the video disc player 1 according to the prior art can be established. Further, if the video disc recorded with the video signal S.sub.ADD is reproduced on a video disc player intended for exclusive use therewith so as to reproduce luminance information in the frequency band higher than the chroma band, it is possible to improve the resolution of the resulting displayed picture, as compared with the picture obtained from the standard composite video signal.
However, in the signal processing operation described above with reference to FIG. 3, a signal component of the luminance signal S.sub.YK is suppressed by the operation of the bandpass filter 11, the comb-type filter circuit 10 and the subtracting circuit 12 so that the luminance signal S.sub.YK is frequency-interleaved with the chroma signal S.sub.CK in the signal S.sub.ADD. Therefore, luminance information in the oblique or slant direction is dropped-out of the video signal S.sub.ADD within the chroma band. As a result, even though the luminance signal is extended to a high frequency band, the resolution of the displayed picture will not be greatly enhanced from the visual standpoint. In other words, although a component video signal including a wide band luminance signal is recorded, it is difficult to obtain a picture whose image quality is improved to the extent that would be realized by effectively utilizing the characteristics of the component video signal.